[vlc-devel] commit: stream: Add a new method for buffering access: A*Immediate method. (Pierre d'Herbemont )

Rémi Denis-Courmont rdenis at simphalempin.com
Thu Jun 5 21:29:32 CEST 2008

Le jeudi 5 juin 2008 22:08:05 Pierre d'Herbemont, vous avez écrit :
> However, nowadays caching at our level doesn't seems to have a big
> impact (we are only caching at most 4Mo), and the kernel doesn't seem
> to trash that much packet, plus disk cache has increased.

4 Mb is a lot more than the "bandwidth" of typical network jitter. 0 Mb is 
infinitely less.

Even sitting idle, my cable modem connection shows about 25ms of packet delay 
variation. That's more than the typical network packetization time (20 ms), 
which is also an intrinsic latency. For audio, 50 ms is not neglectible.

Using TCP, the jitter will be a lot longer due to head-of-line blocking.

Using wireless networking will also increase delay variation.

> I think that this caching may have been useful 10 years back, but is
> not anymore.

For disk I/O, it may be irrelevant because the hardware and the operating 
system read ahead. But VLC caching has hidden packet delay variation which is 
inherent to packet switched network (IP). Sure, we could cache a lot less, 
typically some tens of milliseconds, but we can't remove caching.

Rémi Denis-Courmont

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